ci: add GitHub Actions pipeline for linting and Pester tests

[ndomako10]

Summary

Add a GitHub Actions workflow that runs on every push and pull request to main, ensuring scripts are lint-clean and all Pester tests pass before changes are merged.

Proposed workflow

.github/
  workflows/
    ci.yml

Triggers

• push to main
• pull_request targeting main

Jobs

Job	Steps
lint	Run PSScriptAnalyzer against scripts/ — fail on any error-severity finding
test	Install Pester, invoke Invoke-Pester from repo root — fail if any test fails or the suite errors

Runner

Must use windows-latest — WinRT APIs required by Rename-Photos.ps1 are unavailable on Linux/macOS runners (refs #4).

Acceptance criteria

• Workflow file present at .github/workflows/ci.yml.
• Both jobs run on push and PR to main.
• PSScriptAnalyzer errors cause the lint job to fail.
• A failing Pester test causes the test job to fail.
• A passing run produces a green check on the PR/commit (unblocks merging).

Dependencies

• Depends on test: add Pester test suite for Rename-Photos and Build-Trips #4 (Pester suite must exist before the test job is meaningful).